Non-vitamin K antagonist oral anticoagulants: considerations on once- vs. twice-daily regimens and their potential impact on medication adherence.

Suboptimal medication adherence is a widespread problem in ambulatory care of chronic diseases, with deviations in either direction from the prescribed dosing regimen. For the non-vitamin K antagonist oral anticoagulants (NOACs), such deviations occur and can lead to bleeding or clotting, as suboptimal adherence involves temporary periods of either overdosing or underdosing. In this expert review, we discuss: (a) the proper definition of adherence in terms of its three elements: initiation, implementation, and discontinuation; (b) how adherence is reliably and accurately measured and (c) successfully enhanced, to achieve and maintain safe and effective levels of NOAC-based anticoagulation. We also discuss the comparative effects of prescribing the same total daily dose, given either once-daily or as half-strength twice-daily doses. Because NOACs have plasma half-lives of ∼12 h, the twice-daily dosing regimen is less prone than the once-daily dosing regimen to hazardously high peaks or hazardously low troughs in anticoagulant concentrations and associated actions. As in other fields of oral drug treatment, the continuity of drug action is greater with twice-daily than with once-daily dosing, despite the fact that a few more doses are skipped with twice-daily than with once-daily dosing. This paradox is explained by the disproportionately greater impact on drug action of skipping a once-daily than a twice-daily dose. Integration of these principles into real-world medication management is the next step in the improvement of oral anticoagulation.